1. Field of the Invention
The present invention relates to a color chart for color adjustment, and to a color adjusting method.
2. Description of the Related Art
Endoscopes are in wide use in the medical field. Point light sources of illuminating sections provided in the vicinities of imaging sections of color endoscopes illuminate the interiors of body cavities during imaging using endoscopes. Obtained images are reproduced by color monitors, color printers and the like.
Observation and examination of the interiors of body cavities are based on images obtained by endoscopes. Therefore, it is desirable for the images to be output in colors as close to the actual colors as possible. However, different endoscopes have different color imaging ranges and color reproduction ranges. Accordingly, different color properties are exhibited by each endoscope.
In addition, point light sources provided in the vicinities of imaging sections of color endoscopes are employed to illuminate the interiors of body cavities during imaging. However, it is not possible to uniformly illuminate the entirety of the interior of a body cavity with a point light source. Therefore, a phenomenon called “peripheral light loss”, in which light is insufficient toward the outer periphery of an imaging lens and the periphery of images become dark, occurs. Further, wide angle lenses having short focal distances are utilized in the imaging sections of color endoscopes, in order to image the narrow interiors of body cavities. Therefore, distortion, in which straight lines are imaged as curves, occurs as well.
For example, in the case that a latticed color chart is imaged, the shapes of the colored regions that constitute the color chart are changed by distortion, and may become “barrel-shaped”, in which the center portion is swollen, or “bobbin-shaped”, in which the center portion is constricted. In addition, the image of the color chart is output such that the peripheral portion is darker than the central portion thereof, due to the aforementioned peripheral light loss. There is a possibility that the distortion and/or the peripheral light loss may cause erroneous judgments during color adjustment.
Japanese Unexamined Patent Publication No. 2005-043105 proposes a method for color adjustment for output of images obtained by endoscopes through color printers and color monitors. In this method, a color chart comprising radially spreading fan shaped colored regions is employed, to enable color adjustment which is not influenced by peripheral light loss or distortion.
However, the influence caused by peripheral light loss and distortion cannot be completely eliminated, even if the aforementioned color chart comprising fan shaped colored regions is employed. For this reason, the position within the color chart and changes in brightness cannot be accurately judged based on obtained images, and exact color matching cannot be performed.